Heating, ventilation, and/or air conditioning (HVAC) systems are often used to control the comfort level within a building or other structure. Many HVAC systems include a controller that activates and deactivates one or more HVAC units or components of the HVAC system to affect and control one or more environmental conditions within the building. These environmental conditions can include, but are not limited to, temperature, humidity, and/or ventilation. In many cases, such an HVAC controller may include, or have access to, one or more sensors, and may use parameters provided by the one or more sensors to control the one or more HVAC components to achieve desired programmed or set environmental conditions.
An HVAC controller may be equipped with a user interface that allows a user to monitor and adjust the environmental conditions at one or more locations within the building. With more modern designs, the interface typically includes a display panel, such as a liquid crystal display panel, inset within a housing that contains a microprocessor as well as other components of the HVAC controller. In some designs, the user interface may permit the user to program the controller to activate on a certain schedule determined by the user. For example, the interface may include a routine that permits the user to change the temperature at one or more times during a particular day and/or group of days. Such a programmable schedule may help reduce energy consumption of the HVAC system by changing the setpoint to an energy saving set back temperature during certain times, such as when the building or space is expected to be unoccupied or when the occupants are expected to be sleeping.
When a programmable schedule is employed, and because it is not physically possible to warm up or cool down the space instantaneously to match the programmable schedule, the HVAC controller may be configured to command the HVAC unit(s) (furnace. air conditioner, etc.) to begin changing space temperature well before a scheduled set point change. For example, if an upcoming setpoint is scheduled to change from 68 degrees to 72 degrees at 6:00 AM, the HVAC controller may activate a furnace or the like at 5:30 AM so that the temperature in the building reaches the desired setpoint of 72 degrees at about the desired setpoint time of 6:00 AM. This is often referred to as “recovery” or “setpoint recovery”.
Energy is supplied to most HVAC systems by one or more utilities, such as an electric utility and/or a gas utility. During peak demand periods, such as during hot summer days, such utilities may vary the rates that they charge for energy. Customers may wish to modify their energy consumption in response to these varying rates in order to reduce their energy bills. What would be desirable is a new HVAC controller and control methods that can help customers modify their energy consumption during peak or anticipated peak demand periods in concert with other HVAC system control objectives.